High-frequency cables, in particular coaxial cables, are used to transmit a high-frequency power generated at a fundamental frequency (also known as working frequency) from a high-frequency generator to a matching network (matchbox). The high-frequency power is transmitted from the matching network to a load, for example to a plasma chamber. If the matching network is unable to match the output resistance of the high-frequency generator with the load resistance, then some of the power is reflected on the load due to the mismatch. In this case, power is produced at harmonic frequencies of the fundamental frequency. Power at these frequencies passes through the matching network and the high-frequency cable and arrives at the high-frequency generator.
In the case of harmonic frequencies, the load (the plasma), an electrode, the matching network, the high-frequency cable and an output circuit of the high-frequency generator act as reactance elements with a high intrinsic quality. The excitation by the harmonics, caused by the reflection on the load (for example 100 W effective power of the harmonics with 10 kW power at the working frequency) can thus cause resonances with a high reactive power (for example 10 kVA). This reactive power represents an additional load on the high-frequency cable between high-frequency generator and matching network. This problem applies in particular to so-called dual frequency systems, since these systems have a particularly large number of reactance elements (two high-frequency generators, HF cables and impedance-matching networks with filters). The loading of the high-frequency cable with reactive power can result in failure of the high-frequency cable.